As people offer tributes to dead ancestors and China's "revolutionary martyrs" for the annual Qingming Festival, social media influencers on Beijing's payroll are working overtime.

Key points:

There is heightened anxiety around mass commemoration days in China

2019 marks 30 years since the Tiananmen Square massacre, and 100 since the May Fourth Movement

Both were mass student protests — but one is remembered, and the other forgotten

The annual "tomb-sweeping" festival kicked off yesterday in China, an event that sees families visit and clean the graves of loved ones or respected former leaders and martyrs, leaving them food and wine and even burning paper versions of valuable items their relatives may want in the afterlife.

But back in the realm of the living, it's a period of heightened anxiety.

Qingming sees a spike on social media of what researchers call "astroturfing": that is, pro-Government posts and comments — supposedly from grassroots supporters of the Chinese Communist Party (CCP) — published in a coordinated manner to drown out online discussions.

Harvard and Stanford University researchers estimate some 450 million of these fake social media posts were published in China every year, adding that they peaked around periods of mass commemorations.

"That's because of the concern that popular unrest, and collective action, might be mobilised around holidays or days where there's a particular memory," Tom Sear, a cyber security expert from the University of NSW's Australian Defence Force Academy, told the ABC.

"There's concern that people will begin to talk about those [who] were killed on June 4 in Tiananmen Square."

May 4, 1919: Youth Day — How to celebrate a student uprising

Next month, China will celebrate the 100th anniversary of the May Fourth Movement, a multi-faceted and complicated event that saw thousands of Beijing university students march to Tiananmen, which hadn't yet been developed into a square.

China's 2019 anniversaries:

March 17: 60 years since the Dalai Lama fled Tibet

April 25: 20 years since the Falun Gong sit-in protest, which eventually led to the group's repression

May 4: 100 years since the May Fourth Movement

June 4: 30 years since the Tiananmen Square massacre

July 5: 10 years since the Urumqi riots in Xinjiang Autonomous Region

October 1: 70 years since the founding of the People's Republic of China

December 20: 20 years since Macau was transferred by Portugal to Chinese rule

The student protest was sparked by the Treaty of Versailles, signed in Paris following the end of the First World War, which saw former German colonial territories in China handed over to Japan.

It was an expression of nationalism, a revolt against Japanese imperialism and a rejection of Confucianism: but it was also a time when Western ideas like Marxism, liberalism and democracy were being put forward as solutions to China's problems.

Several leaders of the May Fourth Movement would later go on to play a part in the founding and birth of the CCP, and May 4 is celebrated as Youth Day.

The movement promoted the widespread dissemination of Marxist theory and democratic ideas in China and laid the groundwork for the establishment of the CCP's ideologies and cadres.

But in the 100 years since the 1919 protests, Chinese governments of different persuasions have all struggled with one simple paradox: How do you celebrate a student uprising, without endorsing a future student uprising?

"If May Fourth was to occur today, it would be called an emergency event — it's a collective action on the ground which might threaten the CCP," Mr Sear said.

Support for liberalism and Western ideas expressed through the movement have been removed from commemorations of the event.

Even the rejection of Confucianism — which was a feature of the celebration during the Mao era — is now downplayed, as the Communist Party seeks to promote Chinese history and culture both at home and abroad.

Jeff Wasserstrom from the University of California, a historian with a focus on Chinese student protests, said even though May 4 celebrates an act of youthful revolt, authorities are at pains to stress that modern day young people have no reason to take to the streets.

"[The CCP] has had this kind of narrative that you should admire the youth of 1919, but now China is in a different phase," he said

"So now what you need to do is put your energy, your passion, to use in another direction, in the channelling of this kind of nationalist building up of the state.

June 4, 1989: Tiananmen Square — A silent anniversary

The student protesters of June 4, 1989 — who in part saw themselves as embodying the spirit of the original May 4 protests and initially considered to go out on that day — bore the brunt of this contradiction.

Their deaths will not be commemorated in China, at least not openly. Censorship has seen the protests, and the subsequent bloody crackdown, erased from Chinese history.

"It's really only people … who actually physically remember the event, who are able to counter the narrative because it has been deleted from history," Mr Sear said.

The families of those killed are not even able to remember their lost loved ones freely.

The organisation Tiananmen Mothers, an association for family members of students killed in 1989, say they are placed under surveillance, monitored or forced to travel every year at the beginning of June.

Campus crackdowns ahead of anniversaries

Other signs of heightened anxiety heading towards May 4 and June 4 can be found on the campuses of two of China's most prestigious universities.

Late last year Zhang Shengye, a student at Peking Universityin Beijing who had been involved in labour activism, was disappeared — a group of men reportedly bundled him into a car while he was on campus.

The last couple of weeks also saw Tsinghua University suspend prominent law professor Xu Zhangrun, who wrote a widely shared essay last year critical of President Xi Jinping's leadership.

Professor Wasserstrom said Mr Xu was not unlike the professors who inspired the student protesters back in 1919, making his suspension so close to the May Fourth centenary all the more ironic.

"Xu Zhangrun is a critical intellectual who is now being disciplined … at this exact moment that we're heading to the 100th anniversary of an event, which along with being an anti-imperialist protest, has sometimes been remembered as a time of criticising the authorities," he said.

He said the crackdown on both student activism and critical academics has led to a new low point for intellectual freedom in China.

"It's a really bleak moment. It is the most distressing moment for these kinds of issues, certainly since the period right after the 1989 massacre," Professor Wasserstrom said.

"In some ways it's almost a more chilling moment, because in that case something dramatic had happened.